1. Technical Field
The present invention relates to an electronic device, a method of manufacturing an electronic device, and an oscillator.
2. Related Art
MEMS (Micro Electro Mechanical Systems) is one of micro structure formation technologies and refers to a technology of forming minute electromechanical systems on the order of micrometers and resulting products.
Major devices manufactured by the MEMS technology include vibrators, sensors, and actuators. As the MEMS devices, many devices having movable parts and reading out changes of capacitance due to minute displacement of the movable parts as signals have been known. In the MEMS devices, the displacement of the movable parts are excessively small and gasses including air that inhibits displacement cause reduction in performance and reliability of the devices. For example, it has been known that performance including frequency accuracy and sensitivity of vibrators, pressure sensors, etc. is remarkably improved when the resistance due to the gases such as the air is reduced, and it is desirable that the gases surrounding the MEMS devices are as little as possible. Accordingly, a method of improving device characteristics by placing MEMS devices in cavity parts under reduced pressure and air-tightly sealing them has been studied. Further, an attempt to improve the degree of vacuum within the cavity parts by a sealing method, a sealing structure, or the like has been made.
For example, Patent Document 1 (JP-A-2008-114354) discloses an electronic device having a coating structure that defines a cavity part in which a functional device such as an MEMS device is placed. In the electronic device of Patent Document 1, the coating structure has a multilayered structure including interlayer insulating films and wiring layers and forms an upper coating part (coating layer) that coats the cavity part from above by a part of the wiring layer.
However, in the electronic device of Patent Document 1, for example, when a protective resin including polyimide used for mounting on an electronic substrate is applied, the coating layer that coats the cavity part from above may bend due to pressure of the application. Further, for example, the coating layer that coats the cavity part from above may bend due to pressure of dicing when chipping and pressure when the rear surface of the substrate is ground. When the coating layer bends, a problem that the degree of vacuum within the cavity part becomes lower or, in the worst case, a problem that the coating layer comes into contact with the functional device may occur.